1. Field of the Invention
The present invention relates to a control apparatus for a drive system, in which a torque transmission element such as a belt type continuously variable transmission or a traction type continuously variable transmission is connected to the output side of a power source activated to output a torque when fed with an energy such as a fuel.
2. Related Art
A continuously variable transmission, as adopted in a vehicle or a variety of power transmission mechanisms, is constructed to change the speed of a mating side, to which a torque is to be transmitted, by changing the radii of torque transmitting portions between rotary members. Specifically, the belt type continuously variable transmission is constructed to change the groove widths of an input side pulley and an output side pulley, on which a belt is made to run, so that the pulley radii at the portions gripping the belt, i.e., effective radii can be continuously changed by reducing the groove width of one pulley while increasing the groove width of the other pulley. Thus, the continuously variable transmission is constructed to change the ratio of the speeds between the input side pulley and the output side pulley, i.e., the gear ratio continuously.
On the other hand, the traction type continuously variable transmission, as also called the toroidal type continuously variable transmission, is constructed by gripping a power roller or a transmission member between a pair of discs having toroidal faces on their confronting faces and by tilting the power roller with respect to the center axis of rotations of the discs so that the gear ratio may be continuously changed by changing the radii of the contact position of the power roller with the input disc through an oil film and the contact position of the power roller with the output disc through an oil film from the center axis of rotations.
For the continuously variable transmission of this kind, therefore, it is necessary to form the portions, at which the torque is transmitted, into continuously smooth faces. Moreover, the transmission of the torque is effected by a frictional force (containing the shearing forces of the oil films) so that the contact pressure between the belt and the individual pulleys or the contact pressure between the discs and the power roller has to be raised according to the torque to be transmitted. Moreover, the torque transmitting faces of the pulleys or the discs are demanded to have a high surface hardness and a facial precision for enhancing a wear resistance to the flake wear or for smoothing the torque transmission.
When the belt is firmly gripped to increase its tension or when the power roller is firmly clamped by the individual discs, on the other hand, the motive power to be consumed for enhancing the gripping power and the clamping power and the power loss to be inevitably caused according to the torque transmission are increased to cause a deterioration in the fuel economy of the vehicle. Generally in the prior art, therefore, the gripping force of the belt or the clamping force of the power roller is controlled as low as possible within such a range as to cause neither slippage between the pulleys and the belt nor slippage between the discs and the power roller. When the continuously variable transmission is employed as a transmission of the vehicle, for example, the oil pressure for establishing the gripping force of the belt or the clamping force of the power roller is controlled on the basis of the load on the power source, as represented by the throttle opening.
There is a correlation between the load on the power source such as the throttle opening and the input torque to the continuously variable transmission connected to the output side of the power source. When the oil pressure is controlled according to the load on the power source, therefore, the torque demanded can be transmitted without causing the slippage in the continuously variable transmission. This is because the so-called xe2x80x9ccontact pressurexe2x80x9d between the rotary members such as the pulleys or the discs and the transmission member such as the belt or the power roller matches the torque to be transmitted. When the torque to be transmitted abruptly rises, therefore, the frictional force to be established between the rotary members and the transmission member and the shearing force of the oil films may become relatively short to cause the slippage between the rotary members and the transmission member.
This slippage is exemplified by an engine stall while the vehicle is running. Specifically, during the running, a torque for keeping the vehicle speed at that time or an accelerating/decelerating torque is input to the continuously variable transmission. If the engine (or the power source) abruptly stops in that state, however, there is established the so-called xe2x80x9cengine braking statexe2x80x9d, in which the engine is forcibly turned by the running inertial force owned by the vehicle. In this case, the engine has a high inertial force, and a pumping loss is cased by feeding/discharging the air. On the continuously variable transmission disposed in the drive system to the drive wheels or the engine, therefore, there acts a considerably high torque (or a negative torque) than that during the ordinary running.
The oil pressure at that time, i.e., the gripping force (or the clamping force) of the transmission member is the pressure which is set on the basis of the engine load just before the engine stall occurs, so that the torque to be transmitted becomes relatively excessive. As a result, when the engine stall occurs during the running, the transmission torque capacity set in the continuously variable transmission becomes relatively short to cause the slippage between the rotary members and the transmission member. Accordingly, the torque transmission faces of the rotary members such as the pulleys or the discs are worn to cause fatal damages against the continuously variable transmission.
This situation has a tendency to become serious in a hybrid vehicle. Specifically, this hybrid vehicle has a power generator mounted in parallel with an engine, and the electric power may be generated by driving the power generator with the motive power of the engine while the vehicle is run with the output of the engine. When the engine stall occurs in such running state, a braking force (or the negative torque) is established in both the engine and the power generator. This may increase the torque to act on the continuously variable transmission to a higher level.
As a countermeasure for a gas exhaustion in the vehicle, there have been made a variety of proposals. In Japanese Patent Laid-Open No. 2000-60193 (JPA 2000-60193), for example, there is disclosed an apparatus for suppressing the fuel consumption rate by lowering the torque to be employed for the power generation when detected that the fuel became little. The apparatus disclosed has an object to elongate the distance to be traveled with the residual fuel. Therefore, this apparatus can avoid the engine stall in advance but cannot prevent the mechanical damages at the time when the engine stall occurs.
A main object of the present invention is to prevent or suppress the mechanical damages of a torque transmission element of a continuously variable transmission or the like even when a power source connected to the torque transmission element stops abruptly or suddenly.
In order to achieve this object, the invention is characterized by comprising means for controlling the transmission torque capacity of the torque transmission element to a level matching the so-called xe2x80x9cnegative torquexe2x80x9d at the time when the power source stops, if it is predicted or decided that the power source stops suddenly.
In this invention, therefore, when it is predicted that the power source stops due to the exhaustion of energy, there is increased the transmission torque capacity in the torque transmission element connected to the output side of the power source. Even if the power source stops due to the exhaustion of energy to increase the negative torque or the torque to be applied to the torque transmission element, therefore, the transmission torque capacity of the transmission torque element is increased in advance so that the torque transmission element can be prevented in advance from slipping or from being damaged or worn due to the slippage. In other words, without the stop of the power source being predicted, moreover, the transmission torque capacity of the transmission torque element can be set at a relatively low level thereby to improve the transmission efficiency of the torque or to reduce the energy to be consumed for setting the transmission torque capacity.
Moreover, a control apparatus of the invention comprises: first transmission torque capacity setting means for determining the transmission torque capacity of the torque transmission element on the basis of a drive demand for the power source; second transmission torque capacity setting means for determining the transmission torque capacity at the time when the power source stops due to the exhaustion of energy; power source stop judging means for predicting or judging the stop of the power source due to the exhaustion of energy; and transmission torque capacity selecting means for selecting and setting the higher one of the transmission torque capacity determined by the first transmission torque capacity setting means and the transmission torque capacity determined by the second transmission torque capacity setting means, as the transmission torque capacity of the torque transmission element, when the stop of the power source is predicted by the power source stop predicting means.
In the invention, therefore, even when the power source stops due to the exhaustion of energy so that the negative torque, i.e., the torque to be applied to the transmission torque element is increased, the transmission torque capacity of the transmission torque element has a magnitude necessary and sufficient for the torque applied so that the transmission torque element is prevented from excessively slipping or from being damaged or worn due to the slippage. In other words, when the stop of the power source is not predicted or when the transmission torque capacity of the transmission torque element is already sufficiently high, moreover, the transmission torque capacity of the transmission torque element is not further raised thereby to improve the transmission efficiency of the torque or to reduce the energy to be consumed for setting the transmission torque capacity.
Here, in a control apparatus of the invention, the torque transmission element may be a continuously variable transmission having a torque transmission member gripped in a torque transmittable manner between the input side rotary member and the output side rotary member for changing the individual torque transmission positions of the torque transmission member to the individual rotary members thereby to change a gear ratio continuously, and the transmission torque capacity increasing means may be means for boosting the gripping pressure of the torque transmission member by the individual input side and output side rotary members.
With this construction, therefore, when the stop of the power source due to the exhaustion of energy is predicted or decided, the gripping pressure between the individual rotary members and the torque transmission member in the continuously variable transmission is raised. As a result, even when the stop of the power source invites the state in which the high torque is applied to the continuously variable transmission, the transmission torque capacity between the rotary members and the transmission torque member can be made necessary and sufficient. Therefore, it is possible to avoid in advance the slippage between those members and the damage of the continuously variable transmission due to the slippage. In the ordinary state where the stop of the power source is neither predicted or decided, moreover, the pressure between those members is kept at a relatively low level thereby to improve the transmission efficiency of the torque or to reduce the energy to be consumed for setting the transmission torque capacity.
A control apparatus of the invention can comprise a transmission mechanism for connecting the power source and the continuously variable transmission selectively. The control apparatus of the invention may be constructed to predict or decide the stop of the power source due to the exhaustion of energy when the power source and the continuously variable transmission are connected by the transmission mechanism.
With this construction, when the power source is connected to the continuously variable transmission through the transmission mechanism, the stop of the power source due to the exhaustion of energy is predicted or decided. Only when the stopped power source causes the negative torque on the input side of the continuously variable transmission, the stop of the power source due to the exhaustion of energy is predicted or decided. As a result, when the power source stops so that the negative torque on the input side of the continuously variable transmission rises, the transmission torque capacity of the transmission torque element can be set to a necessary and sufficient value to prevent its slippage or its damage due to the slippage in advance.
Moreover, the present invention may further comprise a functional device connected to the input side of the torque transmission element and activated when it receives the torque selectively from the power source, and the transmission torque capacity increasing means mat be constructed to increase the transmission torque capacity of the torque transmission element when the functional device is active.
With this construction, therefore, not only when the stop of the power source due to the exhaustion of energy is predicted or decided but also when the functional device is active, the transmission torque capacity of the transmission torque element is increased. The functional device is activated by the torque of the power source. When the power source stops, the torque to be applied to the input side of the transmission torque element is increased by the torque of the functional device. On the other hand, the transmission torque capacity of the transmission torque element is increased. Even when the power source stops so that the power source and the functional device connected thereto become causes for increasing the negative torque thereby to increase the torque to be applied to the torque transmission element, the transmission torque capacity of the torque transmission element has been increased in advance to prevent the slippage of the transmission torque element and the damage or wear due to the slippage in advance. In other words, in the state where the stop of the power source is not predicted, moreover, the transmission torque capacity of the transmission torque element can be set at a relatively low level thereby to improve the transmission efficiency of the torque or to reduce the energy to be consumed for setting the transmission torque capacity.
A control apparatus of the invention may further comprise a functional device connected to the input side of the torque transmission element and activated when it receives the torque selectively from the power source, and the transmission torque capacity selecting means may be constructed to select and set the higher transmission torque capacity when the functional device is active.
With this construction, not only when the stop of the power source due to the exhaustion of energy is predicted or decided but also when the higher one between the transmission torque capacity based on the drive demand for the power source at that time and the transmission torque capacity determined as one of the case in which the power source stops is set as the transmission torque capacity of the torque transmission element. The functional device is activated by the torque of the power source. When the power source stops, the torque to be applied to the input side of the torque transmission element is increased by the torque of the functional device. On the other hand, the transmission torque capacity of the torque transmission element is necessary and sufficient for the torque applied thereto so that the excessive slippage of the transmission torque element and the damage or wear due to the slippage are prevented in advance. In other words, in the state where the stop of the power source is not predicted or where the transmission torque capacity of the transmission torque element is already sufficiently high, the transmission torque capacity of the transmission torque element is not further raised to improve the transmission efficiency of the torque or to reduce the energy to be consumed for setting the transmission torque capacity.
Still moreover, a control apparatus of the invention may further comprise an oil pump made active independently of the power source for establishing an oil pressure. The torque transmission element may be constructed to raise the transmission torque capacity in accordance with the pressure oil fed, and the transmission torque capacity increasing means may also be constructed to increase the discharge of the oil pump when the stop of the power source is predicted or decided.
With this construction, when the stop of the power source due to the exhaustion of energy is predicted or decided, the discharge of the oil pump is increased, and this increase is executed separately of the drive of the power source. Even when the power source stops, therefore, it is possible to retain the oil pressure or the pressure oil sufficiently for the transmission torque element. Even when the power source stops due to the exhaustion of energy so that the torque to be applied to the input side of the torque transmission element rises, therefore, it is possible to prevent the slippage of the transmission torque element and the damage due to the slippage.
In a control apparatus of the invention, moreover, the power source and the torque transmission element may be mounted on a vehicle, and the transmission torque capacity increasing means may be constructed to increase the transmission torque capacity in accordance with the speed of the vehicle.
With this construction, the transmission torque capacity of the torque transmission element at the time when the power source stops due to the exhaustion of energy is increased according to the vehicle speed. Even when the power source stops to increase the negative torque on the input side of the torque transmission element, therefore, no slippage occurs in the torque transmission element, and the transmission torque capacity of the torque transmission element can be prevented from being increased more than necessary.
According to the invention, furthermore, there is provided a control apparatus for a drive system, in which a continuously variable transmission having a continuously variable gear ratio is connected to the output side of a power source activated by an energy fed from an energy source. The control apparatus comprises power source stop deciding means for deciding the stop of the power source due to the exhaustion of energy on the basis of the change in the gear ratio of the continuously variable transmission.
With this construction, therefore, it is decided on the basis of a change or an unexpected change in the gear ratio that the power source has stopped. As a result, it is possible to decide the stop of the power source including the stop due to the exhaustion of energy highly precisely.
In a control apparatus of the invention, specifically, the power source stop deciding means may be constructed to decide the stop of the power source due to the exhaustion of energy when an upshift for lowering the gear ratio is detected while a downshift for raising the gear ratio is being commanded.
With this construction, when the gear ratio drops even while the command to raise the gear ratio is being executed, there is decided the stop of the power source due to the exhaustion of energy. It is, therefore, possible to decide the stop of the power source due to the exhaustion of energy highly precisely.
Here in a control apparatus of the invention, the power source can be an internal combustion engine for outputting a motive power by burning a fuel.
With this construction, even when the internal combustion engine stops due to the exhaustion of fuel so that the negative torque is cased to act on the torque transmission element by the so-called xe2x80x9cpumping lossxe2x80x9d of the internal combustion engine, it is possible to avoid the slippage of the torque transmission element and the damage due to the slippage and to decide the stop of the internal combustion engine reliably.
In a control apparatus of the invention, the power source can be an internal combustion engine for outputting a motive power by burning a fuel. The functional device may be a power generator for generating an electric power by receiving the torque from the internal combustion engine, and the internal combustion engine and the power generator may be constructed to become causes for generating a negative torque against the torque transmission element when the internal combustion engine stops while being connected directly to the power generator.
With this construction, even when the internal combustion engine stops due to the exhaustion of fuel so that the internal combustion engine and the power generator become causes for generating the negative torque against the torque transmission element, the transmission torque capacity of the torque transmission element is sufficiently high to avoid the slippage in the torque transmission element and the damage due to the slippage.
The above and further objects and novel features of the invention will more fully appear from the following detailed description when the same is read with reference to the accompanying drawings. It is to be expressly understood, however, that the drawings are for the purpose of illustration only and are not intended as a definition of the limits of the invention.